add a relative `OUTPUT_DIRECTORY` parameter to MapCSSParser.jj to allow compilation with Eclipse plugin. It does not replace the need to set an absolute value in build.xml which overrides this one.

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6521 0c6e7542-c601-0410-84e7-c038aed88b3b